It is well known that most polymers contain "impurities", materials that are different from the higher molecular polymer that constitutes the main part of the polymer. These impurities are often low molecular polymer (oligomer) and other impurities used or made in the polymerization process, such as initiator fragments or surfactants. For many polymers, particularly those not containing fluorine, purification can be accomplished by extracting the polymer with a "solvent" which swells the polymer somewhat, and also dissolves the impurities.
Fluorocarbon polymers, particularly perfluorocarbon polymers that have relatively high melting points are not usually purified by extraction, since solvents that swell the polymers and can dissolve oligomers and other impurities are limited.
European Patent Application 472,908 describes such an extraction using fluorine containing solvents. However, all of the solvents used or mentioned in this patent have boiling points below 100.degree. C. In order to reach even moderately warm (80.degree.-100.degree. C.) temperatures the use of a pressure vessel is required. Even then only very small amounts of impurities are extracted.
In the instant invention use of perfluorinated cycloalkanes (PFC) with atmospheric boiling points above about 140.degree. C. allows the extraction to be run without a pressure vessel, and the extraction is faster and more "impurities" can be extracted. The purified polymer can be used in medical devices and in parts for semiconductor manufacturing industry, in both of which uses impurities can be very deleterious.